Data reception device and data distribution system

ABSTRACT

The radio control section  205  notifies a transmission rate that can be currently set up out of the radio channel transmission rates to the transmission rate decision section  207 . The buffer monitoring section  208  monitors an amount of media data stored in the media reception buffer  209  and when the amount of media data stored exceeds a threshold, the buffer monitoring section  208  notifies it to the transmission rate decision section  207 . When information on the radio channel transmission rate from the radio control section  205  shows that the radio channel transmission rate is well within the capacity and when monitoring information from the buffer monitoring section  208  shows that the amount of data stored in the media reception buffer  209  does not exceed a threshold, the transmission rate decision section  207  outputs a request for increasing the transmission rate of the media data to the control signal transmission/reception section  206 . Thus, even if the maximum rate of the radio channel transmission rate that can be set up decreases due to deterioration of a communication environment, it is possible to prevent data play back from being interrupted.

TECHNICAL FIELD

The present invention relates to a data reception apparatus and datadistribution system that receives data from a server and plays back thedata.

BACKGROUND ART

Conventionally, there is a technology called “streaming” fordistributing images like moving images and packet data like speech froma media server on the Internet and receiving and playing back the dataat a mobile station apparatus. According to this streaming technology,through a radio network connected to the Internet and a base stationapparatus connected to the radio network, data such as moving imagesdistributed from a media server is received by a mobile stationapparatus from the base station apparatus and the moving images, etc.,are played back. The mobile station apparatus that has received packetdata such as moving images plays back the data such as the moving imagesreceived from the media server.

In such a streaming technology, a phenomenon called “jitter” occurs inwhich a delay in data reception increases or decreases according to thenetwork condition. When a delay occurs in data reception due to jitter,the data reception rate becomes lower than the data play back rate. Inthis case, if the received data is continued to be played back, it comesto a point at which there is no more data to be played back and the playback is no longer possible, and therefore the mobile station apparatusis provided with a buffer, the received data is temporarily stored inthis buffer, the data is read from the buffer and played back. In thisway, even if some delay occurs in received data, the data stored in thebuffer is played back and it is thereby possible to prevent play back ofdata from being stopped due to the delay of the received data. When playback of data is started for the first time, an operation called“buffering” is performed first whereby a predetermined amount of data isstored in the buffer before the data is played back and the receiveddata is stored in the buffer even after play back of data is started andthe data to be played back is read from the buffer and played back. Therate at which data is stored in the buffer needs to be set equal to orhigher than the rate at which data is read from the buffer to preventdata to be played back from running short during play back.

However, a conventional radio apparatus has a problem that due todeterioration of a communication environment, a maximum transmissionrate that can be set up for a communication channel decreases, the datareception rate falls below the rate at which data is read from thebuffer making it impossible to play back the data.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a data receptionapparatus and data distribution system capable of preventing play backof data from being stopped even when a maximum transmission rate thatcan be set up for a communication channel decreases due to deteriorationof a communication environment.

This object can be attained, when a maximum transmission rate of theradio channel transmission rate that can be set up is higher than therate at which media data is read from a buffer, by requesting the serverto send the media data at a high rate and storing more data in thebuffer when there is enough space for storage.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an outline of a streaming technology according to anembodiment of the present invention;

FIG. 2 is a block diagram showing a configuration of a mobile stationapparatus according to the embodiment of the present invention;

FIG. 3 illustrates an overall operation of the streaming technologyaccording to the embodiment of the present invention;

FIG. 4 illustrates RTSP messages used in steps according to theembodiment of the present invention;

FIG. 5 illustrates a flow chart showing an operation of the mobilestation apparatus according to the embodiment of the present invention;and

FIG. 6 illustrates a relationship between a radio channel transmissionrate, time and an amount of data storage according to the embodiment ofthe present invention.

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment

With reference now to the attached drawings, embodiments of the presentinvention will be explained in detail below. FIG. 1 illustrates anoutline of a streaming technology. First, an overview of the streamingtechnology will be explained. A media server 101 which is the means fordistributing data is principally constructed of a distribution datastorage section 107, a transmission rate incrementing/decrementingsection 108 and a packet transmission/reception section 109. Thedistribution data storage section 107 stores media to be distributed andoutputs the media to the transmission rate incrementing/decrementingsection 108 when a transmission request arrives from a mobile stationapparatus. The transmission rate incrementing/decrementing section 108controls the transmission rate for the data of the media to bedistributed input from the distribution data storage section 107 in sucha way that it becomes equal to the transmission rate requested from themobile station apparatus 106 and outputs the controlled transmissionrate to the packet transmission/reception section 109. The packettransmission/reception section 109 transmits/receives packets to/fromthe mobile station apparatus 106, receives control commands such asdistribution request data from the mobile station apparatus 106 from theInternet 102, packetizes the distribution data whose transmission rateis controlled by the transmission rate incrementing/decrementing section108 and sends the packet data to the mobile station apparatus 106through the Internet 102.

The Internet 102 outputs the distribution data from the packettransmission/reception section 109 to the radio network 104 through agateway 103 and outputs the control command from the radio network 104received through the gateway 103 to the packet transmission/receptionsection 109. The radio network 104 includes a radio network controlsection 110 and the radio network control section 110 includes a radiochannel control section 111.

The radio network control section 110 which is the notification meansoutputs the distribution data output from the Internet 102 to the basestation apparatus 105. When the radio channel control section 111receives a media distribution request from the mobile station apparatus106 from the base station apparatus 105, it sets up a radio channel forthe mobile station apparatus 106, adjusts a radio channel transmissionrate according to the radio situation and outputs the result to the basestation apparatus 105.

The base station apparatus 105 which is the transmission means receivesthe distribution data output from the radio network control section 110and the result of the radio channel transmission rate output from theradio channel control section 111, combines the distribution data andthe result of adjustment of the radio channel transmission rate,converts it to a radio signal and then sends the radio signal to themobile station apparatus 106. On the other hand, the base stationapparatus 105 receives a control command for a distribution request fromthe mobile station apparatus 106 and outputs it to the radio networkcontrol section 110 and outputs the information that the distributionrequest has been received to the radio channel control section 111. Themobile station apparatus 106 receives the distribution data of the mediasent by radio from the base station apparatus 105 and the result ofadjustment of the radio channel transmission rate and sends thetransmission request for the media distribution data to the base stationapparatus 105 through a radio signal.

Then, the configuration of the mobile station apparatus 106 will beexplained using FIG. 2. FIG. 2 shows the configuration of the mobilestation apparatus 106. The mobile station apparatus 106 is constructedof a radio transmission section 201 and an application section 202. Theradio transmission section 201 is principally constructed of an antenna211, a radio transmission/reception section 203, a packettransmission/reception section 204 and a radio control section 205. Theapplication section 202 is principally constructed of a control signaltransmission/reception section 206, a transmission rate decision section207, a buffer monitoring section 208, a media reception buffer 209 and aplay back section 210.

First, the configuration of the radio transmission section 201 will beexplained. The radio transmission/reception section 203 which is thedata reception means applies radio processing to packet data receivedthrough the antenna 211 and outputs the packet data to the packettransmission/reception section 204 and sends packet data input from thepacket transmission/reception section 204 from the antenna 211 to thebase station apparatus 105 by radio. Furthermore, the radiotransmission/reception section 203 sends a signal requesting a setup ofa packet communication channel to be used for distribution of the mediainput from the radio control section 205 and outputs the transmissionrate of the packet communication channel set up and sent from the radionetwork control section 110 to the radio control section 205.

The packet transmission/reception section 204 outputs an applicationcontrol signal out of the received packet data input from the radiotransmission/reception section 203 to the control signaltransmission/reception section 206, and outputs the media data such asan image signal to the media reception buffer 209. Furthermore, thepacket transmission/reception section 204 receives a signal of abuffering time and buffering speed input from the control signaltransmission/reception section 206 and outputs this signal of thebuffering time and buffering speed to the radio transmission/receptionsection 203.

The radio control section 205 which is the monitoring means monitors avariation in the radio channel transmission rate and outputs thetransmission rate of a packet communication channel set up for the radionetwork control section 110 input from the radio transmission/receptionsection 203 to the transmission rate decision section 207.

Then, the configuration of the application section 202 will beexplained. The control signal transmission/reception section 206controls the application section 202 according to the control signal ofthe application input from the packet transmission/reception section204. Furthermore, the control signal transmission/reception section 206outputs a transmission rate change request control command input fromthe transmission rate decision section 207 to the packettransmission/reception section 204.

The transmission rate decision section 207 which is the requesting meansdecides whether or not to request the media server to change thetransmission rate using radio channel transmission rate informationinput from the radio control section 205 and data amount informationstored in the media reception buffer 209 input from the buffermonitoring section 208. That is, when the radio channel transmissionrate is higher than the rate at which the media data is read from themedia reception buffer 209 and the amount of media data stored in themedia reception buffer 209 does not exceed a threshold, the transmissionrate decision section 207 outputs a media data transmission rate changerequest control command to the control signal transmission/receptionsection 206 and when the radio channel transmission rate is lower thanthe rate at which the media data is read from the media reception buffer209 or the amount of media data stored in the media reception buffer 209is equal to or higher than the threshold, the media reception buffer 209outputs no signal to the control signal transmission/reception section206.

The buffer monitoring section 208 monitors the media reception buffer209 and prevents overflow of the buffer, and therefore when an amount ofdata exceeding a threshold is stored in the media reception buffer, itoutputs a signal to the transmission rate decision section 207instructing it to decide an appropriate transmission rate.

The media reception buffer 209 which is the storing means receives andstores the media data of the packet data input from the packettransmission/reception section 204 during the buffering time and startsoutput to the play back section 210 after the buffering is completed.Furthermore, the media reception buffer 209 continues to store mediadata even after play back is started and outputs the media data to beplayed back to the play back section 210 sequentially.

The play back section 210 plays back the image data read from the mediareception buffer 209.

Then, the operations of the media server 101, radio network controlsection 110 and mobile station apparatus 106 in the above describedconfiguration will be explained taking a case where a maximum rate thatcan be set up is 384 kbps and a normal transmission rate of media(hereinafter referred to as “media-specific rate”) is 128 kbps as anexample using FIG. 3 and FIG. 4. FIG. 3 shows the operation of theentire streaming technology and FIG. 4 shows RTSP messages used invarious steps. The steps described in FIG. 4 correspond to the steps inFIG. 3. In the explanations of the operations, the base stationapparatus 105 stands between the radio transmission section 201 andradio network control section 110, and the gateway 103 and Internet 102stand between the radio network control section 110 and the media server101, but explanations thereof will be omitted for convenience ofexplanation.

When the mobile station apparatus 106 receives media data from the mediaserver 101, it uses RTSP which is a control protocol for mediadistribution, but can also use any protocol other than RTSP.

First, the operation from a state in which the mobile station apparatus106 has no media data received from the media server 101 until themobile station apparatus 106 receives media data at a media-specificrate will be explained. The application section 202 of the mobilestation apparatus 106 sends a request signal to the radio controlsection 205 requesting it to set up a radio channel of a maximum of 384kbps (step (hereinafter described as “ST”) 301).

When the radio control section 205 receives the request signal for asetup of 384 kbps from the application section 202, it negotiates withthe radio network control section 110 through the radiotransmission/reception section 203, decides the transmission bit ratewith the radio situation and condition of the radio network taken intoconsideration and sets up a channel of 128 kbps which is amedia-specific rate (ST302). Here, the media-specific rate is a ratethat allows the media data to be read from the media reception buffer209 and played back by the play back section 210. The radio controlsection 205 notifies the transmission rate decision section 207 that thechannel of 128 kbps has been set up (ST303).

Since the media-specific rate of the media requested to be played backis 128 kbps, the application section 202 approves that the channel of128 kbps which is sufficient for play back has been set up. Whennotified that the channel of 128 kbps has been set up, the applicationsection 202 sends a signal requesting the start of a streaming sessionto the media server 101 through a radio transmission section 201(ST304).

Upon receipt of the signal for the start of the streaming session, themedia server 101 decides whether or not to start the session and when itdecides that the session can be started, the media server 101 sends anOK signal indicating that the session has been started to the radiotransmission/reception section 203 (ST305).

Then, the radio transmission/reception section 203 receives the signalindicating that the session has been started and sends the signal to theapplication section 202 through the radio control section 205. Uponreceipt of the signal indicating that the session has been started fromthe radio control section 205, the application section 202 requests themedia server 101 to send the media data through the radio controlsection 205 and radio transmission/reception section 203. In this case,the application section 202 sends a signal of NPT=0- to the media server101 requesting it to send the media data from the start to end or untilthe end is indicated (ST306). When the media server 101 can respond tothe transmission request from the application section 202, the mediaserver 101 sends an OK signal indicating that transmission is possibleto the application section 202 through the radio transmission section201 (ST307). Then, the media server 101 starts transmission of the mediadata to the mobile station apparatus 106 through the radiotransmission/reception section 203 according to an RTSP protocol and inthis way a radio communication starts (ST308).

Thus, when the user moves during the radio communication and there areno more obstacles such as buildings around the mobile station apparatus,the radio environment may be improved. Furthermore, when the number ofother users belonging to the same base station apparatus decreases, theradio resource may increase. In these situations, the radio networkcontrol section 110 controls the radio control section 205 so as toincrease the transmission rate from the transmission rate of 128 kbpsinitially given at the time of channel setup to 384 kbps. Through suchcontrol, the radio network control section 110 intends to improve theefficiency of the radio resources and the number of authorized users.When such a situation occurs, the radio network control section 110performs an operation called “bearer renegotiation” of negotiating withthe radio control section 205 that the transmission rate should beincreased to 384 kbps which is a maximum speed that can be set up duringa communication (ST309).

Then, the radio control section 205 sends a signal indicating that thetransmission rate has been increased to 384 kbps to the transmissionrate decision section 207 (ST310). Then, learning that the rate has beenincreased to 384 kbps, the transmission rate decision section 207outputs PAUSE which is a control command requesting a pause oftransmission of media data from the media server 101 to the controlsignal transmission/reception section 206 and the control signaltransmission/reception section 206 sends it to the radio network controlsection 110 through the packet transmission/reception section 204 andradio transmission/reception section 203 and the radio network controlsection 110 requests the media server 101 to pause the transmission ofthe media data (ST311). Then, the transmission rate decision section 207calculates the speed to be requested to the media server 101 at whichthe data can be received, and since the calculation result is a triplerate, the transmission rate decision section 207 outputs PLAY Speed 3.0which is a control command requesting the transmission of data at atriple rate to the control signal transmission/reception section 206 andthe control signal transmission/reception section 206 sends it to theradio network control section 110 through the packettransmission/reception section 204 and radio transmission/receptionsection 203 and the radio network control section 110 requests the mediaserver 101 to send data at a triple rate (ST312). Then, the media server101 which has received the request for a pause of the transmission ofthe media data in ST311 sends an OK signal indicating its approval(ST313). Then, the media server 101 which has received the request forsending data at a triple rate in ST312 sends an OK signal indicating itsapproval of sending the data a triple rate to the application section202 through the radio transmission/reception section 203 and radiocontrol section 205 (ST314) and the media server 101 changes the datatransmission rate from ×1 rate which is the media-specific rate to atriple rate and continues to send the media data to the mobile stationapparatus 106 (ST315). PAUSE and PLAY Speed 3.0 are transmittedcontinuously, and therefore the period during which the distribution ofthe media data is interrupted is short and this has no influence on theplay back of the media data at the play back section 210.

Here, the reason that the data transmission rate has been changed to thetriple rate will be explained. Since the transmission rate specific tothe media received from the media server 101 is 128 kbps, it is possibleto transmit data at a rate of 384/128=3 on the radio channel having atransmission rate of 384 kbps. Then, when the radio channel situationdeteriorates again, the radio network control section 110 performs abearer renegotiation with the radio control section 205 through theradio transmission/reception section 203 (ST316) and the radio controlsection 205 sends a signal notifying that the channel transmission ratehas been reduced to 128 kbps to the transmission rate decision section207 (ST317). Then, the transmission rate decision section 207 outputsPAUSE which is a control command requesting a pause of the transmissionof the media data from the media server 101 to the control signaltransmission/reception section 206 and the control signaltransmission/reception section 206 sends it to the radio network controlsection 110 through the packet transmission/reception section 204 andradio transmission/reception section 203 and the radio network controlsection 110 requests the media server 101 so as to pause thetransmission of the media data (ST318). Then, the transmission ratedecision section 207 outputs PLAY Speed 1.0 which is a control commandrequesting that the radio channel transmission rate should be returnedto 128 kbps which is a media-specific rate of ×1 to the control signaltransmission/reception section 206 and the control signaltransmission/reception section 206 sends it to the radio network controlsection 110 through the packet transmission/reception section 204 andradio transmission/reception section 203 and the radio network controlsection 110 requests the media server 101 to return the rate to theoriginal transmission rate, that is, rate ×1 (ST319). Then, the mediaserver 101 which has received the request for a pause of thetransmission of the media data in ST318 sends an OK signal indicatingits approval (ST320). Then, in ST319, the media server 101 sends an OKsignal indicating its approval for the request for setting the channeltransmission rate to ×1 to the application section 202 through the radiotransmission/reception section 203 (ST321), changes the channeltransmission rate from rate ×3 to rate ×1 and continues the transmissionof the media data to the mobile station apparatus 106. PAUSE and PLAYSpeed 1.0 are transmitted continuously, and therefore the period duringwhich the distribution of the media data is interrupted is short andthis has no influence on the play back of the media data at the playback section 210.

Then, the operation of the mobile station apparatus 106 in the abovedescribed configuration will be explained using FIG. 5. FIG. 5 is a flowchart showing the operation of the mobile station apparatus 106. Theapplication section 202 requests the media server 101 to send the mediadata at a normal rate (ST501). Then, when the media server 101 starts tosend media data after approving the normal channel transmission rate,the mobile station apparatus 106 receives the media data (ST502). Then,the buffer monitoring section 208 monitors whether the amount of bufferdata stored in the media reception buffer 209 has exceeded a threshold αor not (ST503).

When the amount of the buffer data stored exceeds the threshold α, thebuffer monitoring section 208 continues reception at the transmissionrate of 128 kbps and when the amount of the buffer data stored fallsbelow the threshold α, the buffer monitoring section 208 decides whetherthe channel transmission rate has increased or not (ST504). When thechannel transmission rate has not increased, the buffer monitoringsection 208 continues to receive data at the transmission rate of 128kbps and when the channel transmission rate has increased, the buffermonitoring section 208 decides the transmission rate at which the mediadata is requested to be sent from the media server 101 (ST505) andrequests the radio network control section 110 to change the channeltransmission rate (ST506).

The media server 101 approves the increase of the transmission rate,transmits media data at 384 kbps which is a transmission rate higherthan 128 kbps and the mobile station apparatus 106 receives data at thetransmission rate of 384 kbps (ST507). The buffer monitoring section 208monitors the amount of buffer data during reception at the transmissionrate of 384 kbps and when an amount of buffer data exceeding thethreshold α is stored, the buffer monitoring section 208 requests themedia server 101 to return the channel transmission rate to 128 kbps,returns the transmission rate to 128 kbps and continues to receive data.

On the other hand, when the amount of buffer data falls below thethreshold α, reception at the transmission rate of 384 kbps is stillpossible, and therefore reception at the transmission rate of 384 kbpsis continued (ST508). Then, the radio control section 205 decideswhether the radio channel transmission rate has decreased or not and ifthe channel transmission rate has not decreased, the radio controlsection 205 continues reception at the transmission rate of 384 kbps andwhen the channel transmission rate has decreased, the radio controlsection 205 sends a request to the media server 101 requesting it toreturn the transmission rate to 128 kbps, returns the transmission rateto 128 kbps and continues reception (ST509).

Then, the relationship between a variation of the radio channeltransmission rate and a re-buffering period will be explained using FIG.6. The horizontal axis shows a time (sec) and the vertical axis shows aradio channel transmission rate (kbps). At time t0, the mobile stationapparatus 106 starts to receive media data from the media server 101. Attime t1, the amount of data in the media reception buffer 209 reaches xbits which is the number of bits with which play back is started andplay back of media is started. From time t1 at which play back of mediais started onward, media data is read from the media reception buffer209 at a constant speed of 128 kbps, and therefore when the receptionrate of the media data is 128 kbps, the media data stored in the mediareception buffer 209 never decreases. On the other hand, when thereception rate of the media data is less than 128 kbps, the media datastored in the media reception buffer 209 decreases.

From time t0 to time t2, the radio channel transmission rate 601 isfixed at 128 kbps which is the same as the rate at which the media datais read from the media reception buffer 209, and therefore the amount ofmedia data stored in the media reception buffer 209 remains fixed at xbits. At time t2, the radio control section 205 informs the transmissionrate decision section 207 that the radio channel transmission rate willbe increased to 384 kbps.

The transmission rate decision section 207 confirms that the mediareception buffer 209 is empty and sends an RTSP control commandrequesting that the transmission rate should be changed to a triple rateto the media server 101 through the control signaltransmission/reception section 206 and radio transmission/receptionsection 203. In this case, the radio channel transmission rate has beenincreased to 384 kbps and the media-specific transmission rate is 128kbps, and therefore the transmission rate to be requested is calculatedas 384/128 kbps=3. Therefore, media data can be received at a triplerate from time t2 on, and therefore data with additional y bits can bestored in the media reception buffer 209 from time t2 to time t3 duringwhich the radio channel transmission rate 601 is 384 kbps and the amountof media data stored in the media reception buffer 209 exceeds x bits.Then, at time t3, the radio control section 205 notifies thetransmission rate decision section 207 that the radio channeltransmission rate has been returned to 128 kbps.

Then, the transmission rate decision section 207 immediately requeststhe media server 101 through the control signal transmission/receptionsection 206 and radio transmission/reception section 203 to return thetransmission rate to 128 kbps. From time t3 to time t4, the radiochannel transmission rate 601 is 128 kbps which is the same as the rateat which media data is read from the media reception buffer 209, butbecause there are y bits stored in the period from time t2 to time t3,the amount of media data stored in the media reception buffer 209 fromtime t3 to time t4 exceeds x bits.

At time t4, the radio control section 205 notifies the transmission ratedecision section 207 that the radio environment has further deterioratedand the radio channel transmission rate has fallen to 64 kbps. In thiscase, since the radio channel transmission rate of 64 kbps is smallerthan the rate of 128 kbps at which media data is read, the media datastored in the media reception buffer 209 decreases and all the data of xbits is consumed at time t5. However, because y bits were stored in themedia reception buffer 209 from time t2 to time t3, it is possible tocontinue to play back media. From time t4 to time t6, the radio channeltransmission rate 601 is 64 kbps and the radio channel transmission rate501 returns to original 128 kbps at time t6. After all, from time t4 totime t6, the radio channel transmission rate is lower than the rate atwhich the media data is read from the media reception buffer 209, andtherefore the amount of media data stored in the media reception buffer209 falls z bits short. However, since the shortfall of z bits isgreater than x bits and smaller than (x+y) bits, play back of media isnot interrupted due to the shortfall of media data and remainsuninterrupted until all the (x+y) bits are consumed.

From time t0 to time t6, the total number of bits of the media datastored in the media reception buffer 209 is (x+y+w) bits. Furthermore,when the radio channel transmission rate also becomes 128 kbps or abovefrom time t7 on, the media data is stored in the media reception buffer209 at a rate of 128 kbps or above.

Thus, according to the radio apparatus of this embodiment, the radiotransmission section 201 monitors the radio channel transmission rateand when the radio channel transmission rate exceeds the media-specificrate, the radio transmission section 201 notifies it to the applicationsection 202, the application section 202 requests the radio channelcontrol section 111 to increase the channel transmission rate so thatmore media data is stored in the media reception buffer 209 while thechannel transmission rate is well within the capacity, and thereforeeven if the channel transmission rate falls short of the media-specificrate, it is possible to prevent the media reception buffer 209 fromrunning short of media data and failing to play back the media data.

This embodiment has assumed that the media-specific rate is 128 kbps andthe transmission rate is increased to 384 kbps when media data isreceived at a high rate, but in the case of the media-specific rate andhigh-speed reception, the rate can be arbitrarily changed according tothe communication environment and the type of media. Furthermore, whenit is possible to setup the radio channel transmission rate to up to 384kbps, this embodiment assumes that the transmission rate of the mediadata is increased to 384 kbps, but it is also possible to set thetransmission rate to any rate other than 384 kbps if it is not lowerthan 128 kbps and not higher than 384 kbps. Furthermore, it is alsopossible to use a fixed communication terminal apparatus instead of themobile station apparatus 106. Furthermore, the above describedembodiment decides the timing for returning the rate from 384 kbps to128 kbps based on whether the amount of data stored in the mediareception buffer 209 exceeds a threshold or not, but it is also possibleto calculate the time during which media data can be stored in the mediareception buffer 209 from the transmission rate that can be set up onthe radio channel and media-specific rate and receive data at 384 kbpsfor the calculated time.

As described above, even if a maximum rate of the radio channeltransmission rate that can be set up decreases due to deterioration of acommunication environment, the present invention prevents data play backfrom being interrupted.

This application is based on the Japanese Patent Application No.2002-117659 filed on Apr. 19, 2002, entire content of which is expresslyincorporated by reference herein.

INDUSTRIAL APPLICABILITY

The present invention is preferably applicable to a data receptionapparatus and data distribution system which receives and plays backdata distributed from a server.

1. A data reception apparatus comprising: a data reception section thatreceives data from a server; a storage section that stores the datareceived by the data reception section; a reading section that reads thedata from the storage section; a play back section that plays back thedata read from the reading section; a monitoring section that monitors avariation in a radio channel transmission rate comprising a maximum datatransmission rate that can be set in a radio channel set up for acommunicating party; and a requesting section that, when the radiochannel transmission rate is equal to or higher than a media specificrate comprising a rate at which the play back section reads data fromthe storage section and plays back the data, requests the server totransmit subsequent data at a rate equal to or higher than the mediaspecific rate.
 2. The data reception apparatus according to claim 1,wherein the requesting section requests the server to transmit thesubsequent data at the rate equal to or higher than the media specificrate according to an amount of data stored in the storage section. 3.The data reception apparatus according to claim 1, wherein, when anamount of data stored in the storage section is smaller than a thresholdand the radio channel transmission rate is equal to or higher than therate at which the data is read from the storage section, the requestingsection requests the server to transmit the subsequent data at a rateequal to or higher than the rate at which the data is read from thestorage section.
 4. The data reception apparatus according to claim 3,wherein the requesting section requests to the server a rate determinedby dividing the radio channel transmission rate changed by themonitoring by the monitoring section, by the rate of reading the data.5. The data reception apparatus according to claim 1, wherein, when anamount of data stored in the storage section is equal to or higher thana threshold, the requesting section requests the server to transmit thesubsequent data at the same rate as the rate at which data is read fromthe storage section.
 6. The data reception apparatus according to claim1, wherein the requesting section requests the maximum rate of the radiochannel transmission rate that can be set.
 7. A communication terminalapparatus provided with a data reception apparatus, wherein the datareception apparatus comprises: a data reception section that receivesdata from a server; a storage section that stores the data received bythe data reception section; a reading section that reads the data fromthe storage section; a play back section that plays back the data readfrom the reading section; a monitoring section that monitors a variationin a radio channel transmission rate comprising a maximum datatransmission rate that can be set in a radio channel set up for acommunicating party; and a requesting section that, when the radiochannel transmission rate is equal to or higher than a media specificrate comprising a rate at which the play back section reads data fromthe storage section and plays back the data, requests the server totransmit subsequent data at a rate equal to or higher than the mediaspecific rate.
 8. A data distribution system comprising: a distributionsection that distributes data; a transmission section that converts thedata distributed by the distribution section to a radio signal andtransmits the radio signal; a reception section that receives the datatransmitted by the transmission section; a storage section that storesthe data received by the reception section; a reading section that readsthe data stored in the storage section from the storage section; a playback section that plays back the data read from the storage section bythe reading section; a monitoring section that monitors a variation in aradio channel transmission rate based on a notification from anotification section that notifies a variation in the radio channeltransmission rate comprising a maximum data transmission rate that canset in a radio channel set up for the transmission section; and arequesting section that, when the radio channel transmission rate isequal to or higher than a media specific rate at which the play backsection reads data from the storage section and plays back, requests thedistribution section to transmit subsequent data at a rate equal to orhigher than the media specific rate.
 9. A data reception methodcomprising: receiving data from a server; storing the received data;reading the stored data; playing back the read data; monitoring avariation in a radio channel transmission rate comprising a maximum datatransmission rate that can be set in a radio channel setup for acommunicating party; and when the radio channel transmission rate isequal to or higher than a media specific rate comprising a rate at whichthe stored data is read and played, requesting the server to transmitsubsequent data at a rate equal to or higher than the media specificrate.